In broadband access networks, besides a Point to Point Protocol over Ethernet (PPPoE) mode based on Ethernet, a Virtual Local Area Network (VLAN) mode and an 802.1 x authentication mode which are very popular at present, a Point to Point Protocol over ATM (PPPoA) mode has been used all along. In the PPPoA access mode, a Point to Point Protocol (PPP) call is initiated by a PPPoA terminal, and a series of PPP access procedures, such as authorization, authentication, Internet Protocol (IP) address assignment and charging, are performed by an ATM Broadband Access Server (BAS). As shown in FIG. 1, the specific steps are as follows:
Step 101: A PPPoA terminal initiates a PPP negotiation to the ATM BAS device, the PPPoA terminal performs a PPP Link Control Protocol (LCP) negotiation with the ATM BAS device to configure and test data links. The PPPoA packet is terminated in the ATM BAS device. The ATM BAS device controls the LCP negotiation procedure, analyzes the PPPoA packet and responds to the PPPoA terminal to complete the LCP negotiation procedure. The controlling methods of negotiation procedures described hereinafter are the same.
Step 102: Based on the result of the LCP negotiation, whether to adopt a Password Authentication Protocol (PAP) or a Challenge-Handshake Authentication Protocol (CHAP) in the authentication procedure is determined. After the LCP negotiation, the PAP or the CHAP authentication procedure starts.
Step 103: After the authentication procedure and the PPPoA terminal passes the authentication, a link is built. The PPPoA terminal performs a PPP Network Control Protocol (NCP) negotiation with the ATM BAS device to choose and configure one or more network layer protocols, and to get authorization instruction of the PPPoA terminal. Then the PPP negotiation is completed. At the same time, the ATM BAS device starts charging for the PPPoA terminal.
Step 104˜Step 105: The PPPoA terminal accesses the Internet, meanwhile, the ATM BAS device terminates the PPPoA packets sent by the PPPoA terminal, that is, removes the protocol headers of the PPPoA packets, extracts the data from the PPPoA packets, and sends the data to the Internet. The extracted data from the PPPoA packets by the ATM BAS device are the specific data contents sent by the PPPoA terminal to the Internet.
Step 106: The PPPoA terminal logs off and notifies the ATM BAS device, the ATM BAS device stops charging for the PPPoA terminal and terminates the access to the Internet of the PPPoA terminal.
The Ethernet achieves a great success by equally super fast transmission rate and lower networking cost than the ATM along with development of the Ethernet technology. ATM Digital Subscriber Line Access Multiplexer (DSLAM) devices start to convert to IP DSLAM devices, and the IP DSLAM devices with more and more powerful functions are adopted in network upgrading.
There are mainly two forms in the existing DSLAM access devices: an ATM DSLAM and an IP DSLAM, where the ATM DSLAM device is a broadband access device whose core is an ATM switch while the IP DSLAM device is a broadband access device whose core is a switch based on the combination of VLAN and Media Access Control (MAC). Broadband access devices can be classified into two categories, that is, frame type and box type, in terms of the device forms, and as shown in FIG. 2, devices of both categories include four components: a main control functional module, a switching functional module, a subscriber interface functional module and a backplane functional module. The subscriber interface functional module is used for providing access interfaces for subscribers, and different subscriber interface functional modules can provide different access methods such as an Asymmetric Digital Subscriber Line (ADSL), a Very High Data Rate Digital Subscriber Line (VDSL), an Ethernet, and a Symmetric High Data Rate Digital Subscriber Line (G.SHDSL). Typically, one broadband access device can provide multiple subscriber interface functional modules, and the subscriber interface functional modules are numbered by a slot number, starting from 0 or 1. Multiple line interfaces for subscriber to access such as 16, 24, or 48 interfaces can be provided in one subscriber interface functional module, and these interfaces are numbered uniformly, starting from 0 or 1. The main control functional module is used for implementing control and administration functions of the broadband access device. The switching functional module is used for implementing traffic converting and processing functions of the whole broadband access device, and for implementing an interface of the network side. The backplane functional module is used for providing connection and communication functions for the above functional modules.
The broadband access device based on the ATM core is one generation of current mainstream type of access device. The broadband access device adopts a switching structure of ATM, that is, both data communication between the subscriber interface functional module and the main control functional module, and the data communication between the subscriber interface functional module and the switching functional module use the ATM bearer, adopting a shared cell bus or an ATM bus interface. At the same time, the switching subsystem is also based on switches of the ATM cells. As shown in FIG. 3A, the specific service procedure is as follows: service data are transmitted from the subscriber interface functional module to the switching functional module by an ATM Virtual Channel (VC) bearer and the cell based bus of the backplane functional module, the switching functional module forwards the service data using a cell based switching method, that is, performs a Virtual Path Identifier (VPI)/Virtual Channel Identifier (VCI) conversion of the ATM VC header, and outputs the service data to a corresponding output port.
Because the ATM technology has stopped developing, the ATM interface bandwidth of mainstream applications has stops at the level of STM-1, 155 Mbps, the bandwidth capacity of STM-4, 622 Mbps and the bandwidth capacity of STM-16, 2.5 Gbps have not been used commercially because of too high interface costs. Meanwhile, demands for the network bandwidth increasingly rise with development of various network services, and the ATM switching network has been unable to meet the demands for larger bandwidth. Mainstream services in networks are now using the IP bearer while the ATM is based on a connection mode. Therefore, the ATM cannot effectively perceive the multiple services on the IP bearer, and thus, cannot effectively guarantee the quality of multiple services. When it comes with an IP Television (IPTV) service, which is a multicast video service of mainstream applications, because of the technical characteristic of a point to point connection of the ATM, configuration and maintenance administration for such a point to multiple points service is rather complex, thus, no commercial network can be built effectively, which makes it impossible to support the development of such mainstream services with the ATM.
As the bandwidth of the ATM core based broadband access device is small, an Ethernet/IP core based broadband access device, which is relatively a new broadband access device at present, is proposed. Because an Ethernet Layer 2(L2)/Layer 3(L3) based switching structure is adopted by an IP broadband access device, a larger switching capability such as 10 Gbps—48 Gbps or even larger can be provided, and also an interface bandwidth of Fast Ethernet (FE)/Gigabit Ethernet (GE), even 10 GE, can be provided. Thus, the bottleneck of bandwidth is resolved. Both the data communication between the subscriber interface functional module and the main control functional module and the data communication between the subscriber interface functional module and the switching functional module are born by the Ethernet, and an FE or a GE connection can be adopted between the subscriber interface functional module and the main control functional module while the switching functional module witches based on the Ethernet. As shown in FIG. 3B, the specific service procedure is as follows:
a service accessed by the subscriber interface functional module is carried by the ATM VC bearer or the Ethernet bearer, and the subscriber interface functional module reorganizes and restores the ATM cells to an Ethernet packet, adds an 802.1Q based VLAN identifier to the Ethernet packet, and then transmits it to the switching functional module by an Ethernet based FE/GE star style bus of the backplane functional module. Then, the switching system forwards the service data based on a switching method combining the VLAN and the MAC addresses or based on the IP addresses, and outputs the service data to a corresponding output port.
Thus, how to support a PPPoA based access method on the IP DSLAM device becomes an urgent problem to be solved.